1. Field of the Invention
This invention relates to an abrasive tape for use in polishing of a magnetic head for a magnetic recording and reproducing apparatus. This invention particularly relates to an abrasive tape for use in polishing of a magnetic head mainly by being moved between two reels.
2. Description of the Prior Art
Video or high grade audio magnetic heads are required to have very smooth tape sliding surfaces. Therefore, in general, in the process of making the magnetic head, the magnetic head is disposed at a predetermined position after rough grinding, and the tape sliding surface of the magnetic head is finished to be smooth by moving an abrasive tape between two reels disposed with the magnetic head intervening therebetween. In general, the abrasive tape comprises a flexible substrate, and a coating film formed on the flexible substrate by applying an abrasive composition containing fine abrasive grains, a binder, and optionally an additive such as a lubricant, which are kneaded together, onto the flexible substrate. Since the substrate of the abrasive tape is flexible, the abrasive tape can accurately polish the tape sliding surface of the magnetic head by snugly fitting to the curved shape thereof.
As the abrasive tape, there has heretofore been known, for example, a cleaning tape as disclosed in Japanese Unexamined Patent Publication No. 53(1978)-102017, which comprises a substrate, and a coating film overlaid on the substrate by applying thereonto an abrasive composition containing, for example, abrasive grains consisting of zinc oxide (ZnO), a binder consisting mainly of a vinyl chloride resin, and various additives such as a curing agent consisting of a polyisocyanate or the like and a lubricant such as silicone oil, which are kneaded together.
Accordingly, it is considered to replace only the abrasive grains by a substance harder than zinc oxide in the aforesaid cleaning tape and to use the tape thus obtained as an abrasive tape.
However, with the abrasive tape formed by using the vinyl chloride resin as the binder, dispersibility of the abrasive grains by the vinyl chloride resin is low, and the abrasive grains often agglomerate and concentrate at a portion of the abrasive tape, thereby causing scratching of the polished surface.
On the other hand, in recent years, magnetic heads formed of Permalloy are used widely. However, Permalloy is a soft and readily corrodible alloy, and therefore the tape sliding surface of the Permalloy magnetic head is readily corroded. With the abrasive tape formed by using the vinyl chloride resin as the binder, hydrochloric acid is readily released from the binder and corrodes the polished surface contacting the abrasive tape. Therefore, the abrasive tape formed by using the vinyl chloride resin as the binder is not suitable particularly in the case where the material which is to be polished is readily corrodible as in the case of the Permalloy magnetic head.